1. Field of the Invention
This invention relates to a vertical pin integrated circuit probing device, and more particularly to an assembly apparatus and method for loading probe pins into a die head assembly of the vertical pin integrated circuit probing device.
2. Description of the Related Art
U.S. Pat. Nos. 6,297,657 and 6,633,175 illustrate vertical pin probing devices and are incorporated by reference as if fully disclosed in their entireties herein.
One type of vertical pin probing devices utilizes a buckling beam die design. As described in U.S. Pat. No. 6,297,657, an integrated circuit or other device under test is supported on a movable chuck. The integrated circuit typically has a pattern or matrix of contact pads to be simultaneously probed by a vertical-pin integrated circuit probing device, such as the probe head sold under the brand name COBRA® by Wentworth Laboratories of Brookfield, Conn. The probing device includes a lower die with a group of holes and an upper die with a group of holes separated by a spacer and carrying multiple vertical pin probes. The die materials are typically made of a plastic insulating material such as those sold under the brand name Delrin®, an acetal resin that is a registered trademark E.I. duPont de Nemours & Co of Wilmington, Del., a low expansion metal such as those sold under the brand name Invar®, a nickel alloy that is a registered trademark of Imphy, S.A., or a ceramic such as silicon nitride.
Each probe pin has a probe tip that protrudes from a hole in the lower face of the lower die and an exposed head that protrudes from holes in the upper side of upper die. Holes containing opposing ends of the vertical probe pins are slightly offset from one another and the probe pins are curved in a snake-like configuration to promote buckling, so as to create substantially uniform contact pressure on the integrated circuit pads despite any slight vertical unevenness or misalignment.
With reference to FIG. 1, a partially-assembled portion of a buckling beam die 10 as known in the prior art includes of a lower die 12, probe pins 14, and an assembly aid film 16. Lower die 12 contains an array of micro-holes 18 into which probe tips 20 are inserted. Assembly aid film 16 contains a matching pattern of micro-holes 22 punched into the film. One edge 24 of a small piece of assembly aid film 16 is adhered, e.g., using tape or similar, to top 26 of lower die 12 so that it is approximately positioned over micro-holes 18. Each probe tip 20 is inserted into one of lower die micro-hole 18, and then probe head 28 is inserted up through a corresponding micro-hole 22 in assembly aid film 16 to hold probe pin 14 in position. This process is continued until each of probe pins 14 are in place. Insertion of probe heads 28 requires lifting assembly aid film 16 to provide sufficient clearance to slip each probe head under the film and up through the proper one of micro-holes 18. As the assembly proceeds, it is necessary to tie down assembly aid film 16 periodically to prevent it from lifting up off probe heads 28 of the contacts that have already been installed. Regardless, assembly aid film 16 occasionally lifts off probe heads 28 resulting in the need for a partial or complete re-assembly. The process of fitting probe heads 28 up through micro-holes 22 in assembly aid film 16 also presents opportunities for each of probe pins 14 to be inadvertently bent.
After each of probe pins 14 have been loaded into lower die 12 and assembly aid film 16, it is necessary to cut the film so that it fits entirely inside an upper die cavity, and to remove the tie-down wires. This process often results in assembly aid film 16 lifting off one or more of probe heads 28, again requiring a partial or complete re-build of the assembly. After assembly aid film 16 has been cut and the wires removed, it is necessary to install an upper die 30. As shown in FIG. 2, this requires aligning upper die 30, which has an array of micro-holes 32 matching the pattern of micro-holes 18 and 22 in lower die 12 and assembly aid film 16, respectively, over array of probe pins 14 such that each of probe heads 28 lines up with a respective one of the micro-holes in the upper die. This is a delicate operation, as typically each of thousands of probe pins 14 must pass through one of micro-holes 32 simultaneously in order to avoid bending probe pins. Consequently, each of micro-holes 32 in upper die 30 are larger than those in lower die 12 and in assembly aid film 16 to facilitate assembly. Also, still referring to FIG. 2, upper die 30 is conventionally made by starting with a round disk of polyimide material of approximately 0.1 inch thickness, and milling out a cavity 34 leaving a thin “web” on the order of 0.010″ thick through which the pattern defining array of micro-holes 32 is drilled. It is often difficult to keep such a thin web of material flat across the array due to unbalanced internal stresses in the material after milling, moisture absorption, etc., and may result in a relatively low yield rate for upper dies.
After upper die 30 is installed, alignment pins (not shown) are inserted to correctly align the upper die with lower die 12 dies, and screws (not shown) are installed to hold the upper and lower dies together. Probe heads 32 are then lapped in order to arrive at a consistent over-all probe pin length throughout the array. One consequence of the lapping process is that lapping debris passes through over-sized micro-holes 32 in upper die 30 and collects on assembly aid film 16 inside the head assembly. This debris is conductive and must be removed to avoid electrical shorting between contacts. It is therefore necessary to remove upper die 30 after lapping in order to adequately remove the debris. The removal of upper die 30 presents a further opportunity for assembly aid film 16 to lift off probe heads 28, requiring a partial or full re-build of the assembly. It also requires upper die 30 alignment and assembly to be repeated, presenting another opportunity for bending probe pins 14 if alignment is not perfect.
One of the advantages of buckling beam technology is repair-ability. Since the probe pins are not permanently bonded to the test electronics, it is possible to replace damaged probe pins rather than discard the entire assembly. The repair process with the conventional design as illustrated in FIG. 2 may be problematic. The repair process requires removal of upper die 30 to gain access to probe pins 14. A damaged one of probe pins 14 is then extracted by pulling it through assembly aid film 16, and re-inserting a new probe pin through the same assembly aid film hole. There are several problems that may arise when using this technique. First, the removal of upper die 30 may cause assembly aid film 16 to lift off one or more of probe heads. Static electricity sometimes results in assembly aid film 16 adhering to the underside of upper die 30 and coming completely off the array, resulting in the need for a complete re-build.
Assuming upper die 30 is successfully removed, any of probe pins 14 that are damaged must then be withdrawn through assembly aid film 16. Since micro-holes 22 in assembly aid film 16 are “tight”, e.g., with a diameter on the order of 0.0001 inch larger than the diameter of typical probe pin 14, the assembly aid film must be slightly torn in order for the probe pin “swage” to pass through the film. This “tugging” on assembly aid film 16 presents another opportunity for the film to lift off of one or more of probe pins 14.
Assuming a damaged one of probe pins 14 is successfully removed and another probe pin inserted, the particular one of micro-holes 22 in assembly aid film 16 is now enlarged, causing potential difficulties in aligning the new probe pin with its associate micro-hole 32 in upper die 30. Also, enlarged one of micro-holes 22 in assembly aid film 16 allows probe pin 14 more freedom of movement, which may allow it to contact a neighboring probe pin in tight tolerance applications resulting in an electrical short circuit.